The effects of pH and ionic strength on the rheological behavior of aqueous suspensions of both crude and purified Wyoming bentonite and natural interstratified illite-smectite from Tunisia were investigated. Flow tests were performed on the four clay suspensions at a 10% clay concentration at different pH values. They showed that the rheological properties were highly sensitive to pH and the nature of the clay. The evolution of the yield stress as a function of pH is characterized by the presence of maxima and minima attributed to changes in the mode of association of the particles. The effect of pH on the behavior of clay suspended in NaCl solutions was also studied. The results show that the presence of NaCl has very little effect on the pH and yield stress values of the four materials.

The effects of humic acid (HA) on the crystallization of precipitation products of Al under mildly acidic to alkaline conditions were investigated. The extent of Al precipitation substantially decreased with increasing HA concentration (0 to 75 µg/ml) in the pH range 6 to 10 during the 80-day aging period. The X-ray powder diffraction (XRD) data show that, at pH 6.0, the amount of pseudoboehmite formed in the systems decreased with the increasing concentration of HA present. The proportion of Al hydroxide polymorphs (gibbsite and bayerite) was greatly influenced by the amounts of HA present in the systems. At pH 6.0 and HA concentration of 37.5 µg/ml, all the precipitation products of Al were noncrystalline. At pH 8.0 and a HA concentration of 12.5 µg/ml, the formation of gibbsite and bayerite was completely inhibited and only pseudoboehmite was evident in the XRD patterns. Further increase in HA concentration (25–75 µg/ml HA) at pH 8.0 resulted in no precipitation of Al, and only a broad peak at ∼3.3 Å, characteristic of HA, was observed. The XRD patterns of the precipitates of Al formed in the absence of HA at pH 10.0 showed the characteristic peaks of bayerite. At pH 10.0, the precipitation products of Al formed even at the HA concentration of 2.5 µg/ml yielded no XRD peaks. Infrared absorption spectra and transmission electron micrographs of the precipitation products of Al formed in the systems studied substantiate the findings obtained by XRD. The data obtained in this study indicate that HA affects the formation of Al hydroxide polymorphs, pseudoboehmites and short-range ordered mineral colloids.

Mobility measurements were made for dry-ground mica particles dispersed in aqueous KCl, Cr(NO3)3, and cetyltrimethylammonium bromide (CTAB) solutions. In the latter solutions charge reversal occurred at about 2 × 10-6 M and 3 × 10-5 M, respectively. Negative zeta potentials in KCl solutions calculated using the Smoluchowski equation are about one third of the corresponding values obtained from streaming potentials and force measurements using mica sheets. Good agreement, however, was obtained when positively charged groups created during grinding were neutralized, and the zeta potentials were corrected according to the procedure of O'Brien and White with an assumed average particle size of 0.25 μm. When the zeta potentials of positively charged particles were corrected in this way, agreement with values calculated from force measurements was also improved.

Montmorillonite-aminocaproic acid complexes (monomer complexes) were prepared by the intercalation of 6-aminocaproic acid to various homoionic (Na+, Ca2+, Mg2+, Co2+, and Cu2+) montmorillonites. Infrared spectra of the monomer complexes indicated that the interaction between the exchangeable cations and the 6-aminocaproic acid increased in the following order: Na-, Ca-, and Mg- < Co- < Cu-montmorillonite-aminocaproic acid complex. Montmorillonite-nylon complexes (polymer complexes) were prepared by thermal treatment of the monomer complexes, which was confirmed by X-ray powder diffraction and infrared spectroscopy the results of which indicated the condensation of 6-aminocaproic acid in the interlayer space.

Thermal degradation of montmorillonite-nylon complexes was studied by thermogravimetry. It was found that the thermal stability of the polymer complexes increased in the following order: Cu- < Co- < Na- < Mg- < Ca-montmorillonite-nylon complex.

It was suggested that the difference in thermal stability depended upon the length of the polymer chain which might be influenced by the interaction between the exchangeable cations and the 6-aminocaproic acid. The activation energy for the thermal degradation of each montmorillonite-nylon complex was obtained, and the value for Cu-montmorillonite-nylon complex was smaller than that for the other cation-exchanged montmorillonite-nylon complexes.

Fe(II)–Fe(III) green rust identified in soil as a natural mineral is responsible for the blue-green color of gley horizons, and exerts the main control on Fe dynamics. A previous EXAFS study of the structure of the mineral confirmed that the mineral belongs to the group of green rusts (GR), but showed that there is a partial substitution of Fe(II) by Mg(II), which leads to the general formula of the mineral: ${[{\text{Fe}}_{1-x}^{2+}{\text{Fe}}_x^{3+}{\text{Mg}}_y{(\text{OH})}_{2+2y}]}^{x+}{[x{\text{OH}}^{-}\cdot m{\text{H}}_2\text{O}]}^{x-}$${[{\rm{Fe}}_{1 - x}^{2 + }{\rm{Fe}}_x^{3 + }{\rm{M}}{{\rm{g}}_y}{({\rm{OH}})_{2 + 2y}}]^{x + }}{[x{\rm{O}}{{\rm{H}}^ - } \cdot m{{\rm{H}}_2}{\rm{O}}]^{x - }}$. The regular binary solid-solution model proposed previously must be extended to ternary, with provision for incorporation of Mg in the mineral. Assuming ideal substitution between Mg(II) and Fe(II), the chemical potential of any Fe(II)-Fe(III)-Mg(II) hydroxy-hydroxide is obtained as: $\text{μ}=X_1{\text{μ}}_{\text{1}}^{\text{o}}+X_2{\text{μ}}_{\text{2}}^{\text{o}}+X_3{\text{μ}}_{\text{3}}^{\text{o}}+\text{R}T[X_1\text{ln}{X}_1+X_2\text{ln}{X}_2+X_3\text{ln}{X}_3]+A_{12}{X}_2(1-X_2)$${\rm{\mu }} = {X_1}{\rm{\mu }}_{\rm{1}}^{\rm{o}} + {X_2}{\rm{\mu }}_{\rm{2}}^{\rm{o}} + {X_3}{\rm{\mu }}_{\rm{3}}^{\rm{o}} + {\rm{R}}T[{X_1}{\rm{ln}}{X_1} + {X_2}{\rm{ln}}{X_2} + {X_3}{\rm{ln}}{X_3}] + {A_{12}}{X_2}(1 - {X_2})$. All experimental data show that the mole ratio X2 = Fe(III)/[Fetotal + Mg] is constrained (1) structurally and (2) geochemically. Structurally, Fe(III) ions cannot neighbor each other, which leads to the inequality $X_2\alpha \raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$3$}\right..$${X_2}\leqslant {\raise0.5ex\hbox{$\scriptstyle 1$}\kern-0.1em/\kern-0.15em\lower0.25ex\hbox{$\scriptstyle 3$}}.$ Geochemically, Fe(III) cannot be too remote from each other for GR to form as Fe(OH)2 and Mg(OH)2 are very soluble, so $X_2\alpha \raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$4$}\right.$${X_2}\geqslant {\raise0.5ex\hbox{$\scriptstyle 1$}\kern-0.1em/\kern-0.15em\lower0.25ex\hbox{$\scriptstyle 4$}}$. A linear relationship is obtained between the Gibbs free energy of formation of GR, normalized to one Fe atom, and the electronegativity ϰ of the interlayer anion, as: μo/n = −76.887ϰ — 491.5206 (r2 = 0.9985, N = 4), from which the chemical potential of the mineral fougerite μ is obtained in the limiting case X3 = 0, and knowing ${\text{μ}}_{\text{1}}^{\text{o}}=-489.8$${\rm{\mu }}_{\rm{1}}^{\rm{o}} = - 489.8$ kJmol−1 for Fe(OH)2, and ${\text{μ}}_{\text{3}}^{\text{o}}=-832.16$${\rm{\mu }}_{\rm{3}}^{\rm{o}} = - 832.16$ kJmol−1 for Mg(OH)2, the two unknown thermodynamic parameters of the solid-solution model are determined as

${\text{μ}}_{\text{2}}^{\text{o}}=+119.18{\text{kJmol}}^{-1}$${\rm{\mu }}_{\rm{2}}^{\rm{o}} = + 119.18\;{\rm{kJmo}}{{\rm{l}}^{ - 1}}$ for Fe(OH)3 (virtual), and A12 = −1456.28 kJmol−1 (non-ideality parameter). From Mössbauer in situ measurements and our model, the chemical composition of the GR mineral is constrained into a narrow range and the soil solutions-mineral equilibria computed. Soil solutions appear to be largely overstaurated with respect to the two forms observed.

This paper aims at characterizing the morphology, texture, and microstructure of three hydrated kaolin rich clays (f < 0.2 μm) from volcanic soils. These clays represent a weathering sequence in which CEC, halloysite content with respect to kaolinite, as well as smectite content in the halloysite-smectite mixed-layer clays decrease with increased weathering. The clay samples were made homoionic (K+ or Mg2+) and hydrated under a low suction pressure (3.2 kPa). After replacing water by a resin, ultrathin sections were cut and examined by TEM. Particle shape varies with increased weathering, as follows: spheroids → tubes → platelets. Higher aggregation and dispersion are observed by TEM after Mg2+ and K+ saturation, respectively, at two levels of the clay-water system organization: intraparticle and interparticle. The microstructure variations induced by the nature of the exchangeable cation become less pronounced with decreasing layer charge of the 2:1 layers. They are thus related here to the presence of smectite layers localized in the halloysite habitus, mostly at the particle periphery. These results show that small amounts of smectite largely affect the organization of clays rich in kaolins at a high water content, and that K+ behaves here as a dispersing ion.

Zeolites having the structures of phillipsite, merlinoite, and gobbinsite were synthesized from clear solutions at 80°C in the system Na2O-K2O-Al2O3-SiO2-H2O and their morphologies, cell parameters, and compositions determined. At 3.5 M silica concentration, the formation of merlinoite (synthetic zeolite W) is favored over the formation of phillipsite (synthetic zeolite ZK-19) by solution conditions of high pH (> 13.6) and low Na/(Na + K) ratios (<0.5).

Using the information obtained from the synthesis experiments, the presence of merlinoite was predicted in sediments from Searles Lake, a saline, alkaline lake in California with ideal physiochemical conditions for its formation. Merlinoite was subsequently discovered to occur in tuffaceous sediments as part of an authigenic silicate zonation pattern from phillipsite → phillipsite + merlinoite → merlinoite → K-feldspar with increasing depth. Because of the close similarities in the physical properties of phillipsite and merlinoite, merlinoite may be much more common as an authigenic mineral than is currently realized.

A series of synthetic goethites containing varying amounts of Si and P dopants were characterized by X-ray powder diffraction, electron diffraction, microbeam electron diffraction, and Mössbauer spectroscopy. Very low level incorporation produced materials having structural and spectral properties similar to those of poorly crystalline synthetic or natural goethite. At higher incorporation levels, mixtures of noncrystalline materials were obtained which exhibited Mössbauer spectra typical of noncrystalline materials mixed with a superparamagnetic component. Microbeam electron diffraction indicated that these mixtures contained poorly crystalline goethite, poorly crystalline ferrihydrite, and a noncrystalline component. If the material was prepared with no aging of the alkaline Fe3+ solution before the addition of Na2HPO4 or Na2SiO3, materials were obtained containing little if any superparamagnetic component. If the alkaline Fe3+ solution was aged for 48 hr before the addition, goethite nuclei formed and apparently promoted the precipitation of a superparamagnetic phase. The Mössbauer-effect hyperfme parameters and the saturation internal-hyperfine field obtained at 4.2 K were typical of those of goethite; however, the Mössbauer spectra indicated that the ordering temperature, as reflected in the relaxation rate and/or the blocking temperature, decreased with increasing incorporation of Si and P. The complete loss of crystallinity indicates that Si and P did not substitute for Fe, but rather adsorbed on crystal-growth sites, thereby preventing uniform crystal growth.

The occurrence of palygorskite in some Tertiary sediments in eastern Saudi Arabia was studied. Mineralogical and chemical analyses were made of samples from two sections several meters thick from the Umm er Radhuma and Dammam Formations of Paleocene and Eocene periods, respectively. Layers of shales were observed within the sections of the dolomitic-calcitic limestone of the Umm er Radhuma Formation and of the dolomitic limestone of the Dammam Formation. After treatment for carbonate removal the shales consisted of more than 95% clay-size particles, most of which were <0.2-μm in size. Palygorskite was the main constituent of some of the shales, with minor amounts of gypsum, soluble salts, and carbonates. The association of gypsum and other salts with palygorskite in the shale suggests that palygorskite formed in closed-basin environments. The presence of palygorskite and the absence of other minerals in the clay fraction of the limestones also suggests that the palygorskite formed under marine conditions.

Aerogels of clays can be prepared by freeze-drying of clay water gels. The mechanical strength of the aerogels is improved by the addition of water-soluble polyelectrolytes to the hydrogels.

The porosity of the powdered aerogels can be adapted to the requirements for adsorbents in gas chromatography by compounding the hydrogels with suitable amounts of polyelectrolytes. Simultaneously, the surface of the clay may be modified by adsorption of polar or cationic organic compounds in order to achieve specific chromatographic separations.

Because of the toughness of the clay-polyelectrolyte aerogels, they can be rolled out to thin sheets which may be applied as chromatographic papers.

Tobermorite, Ca5Si6O16(OH)2·4H2O, is a hydrous calcium silicate that has a layer-type of structure similar to that of the 2:1 clay minerals. In its natural form, tobermorite exhibits little or no exchange for alkali cations; synthetic tobermorites, however, exhibit reversible alkali cation exchange and selective cesium uptake upon a coupled substitution of (Al3+ + Na+) for Si4+. Substituted tobermorites were synthesized using aluminosilicate gels, NaOH, and CaO, in Parr bombs at 175°C for 4 days. Unsubstituted tobermorite was synthesized using quartz and CaO in a Parr bomb at 175°C for 20 hr. Two (Al + Na)-substituted tobermorites showed cation-exchange capacities (CEC) of 77 and 71 meq/100 g, whereas an unsubstituted tobermorite showed a CEC of 12 meq/100 g. The substituted tobermorites exhibited selective Cs exchange from either NaCl or CaCl2 solutions. For example, one substituted tobermorite showed a Cs-exchange coefficient (Kd) of 15,100, whereas unsubstituted tobermorite showed a Kd of only 90 from a 0.02 N CaCl2 solution containing 0.0002 moles/liter CsCl. Exchange isotherms for Na+ ⇋ Cs+ showed that Cs+ is preferred over Na+ throughout the exchange in the (Al + Na)-substituted tobermorites. This group of cation exchangers is expected to find applications in radioactive waste disposal.

The crystalline and osmotic swelling of Na-, Cs-, Mg- and Ca-montmorillonite has been measured in dimethyl sulphoxide and in formamide, N-methyl formamide, dimethyl formamide, N-methyl acetamide and dimethyl acetamide. These liquids have similar dipole moments but their relative permittivities vary appreciably from values less than water to values greater than water.

Na-montmorillonite exhibits osmotic swelling (diffuse double layer development −d(001) ≫ 19 Å) in formamide and N-methyl formamide and Cs gives osmotic swelling behavior in formamide. Cs-montmorillonite in the crystalline swelling region give spacings greater than those found for water with all liquids. Mg- and Ca-montmorillonite did not give spacings greater than 19 Å in any of the liquids studied.

The swelling behavior of montmorillonite is affected by relative permittivity but for liquids with a similar relative permittivity methyl substitution in the molecule may prevent the development of diffuse double layers on the particle surfaces.

Caliche in various forms, namely powdery, nodule, tube, fracture-infill, laminar crust, hard laminated crust (hardpan), and pisolitic crust, is widespread in the Mersin area in southern Turkey. It generally occurs within and/or over the reddish-brown mudstone of the Kuzgun Formation (Tortonian, Miocene) and alluvial red soils of the Quaternary. The mineralogical distribution along representative caliche profiles was examined by X-ray diffraction, scanning electron microscopy, differential thermal analysis-thermal gravimetry, and chemical techniques. Calcite is the most abundant mineral associated with minor amounts of palygorskite in caliche samples, whereas smectite is prevalent mainly in the reddish-brown mudstone and alluvial red soils of the caliche parent materials and is associated with appreciable amounts of palygorskite. These minerals are also accompanied by trace amount of illite, quartz, feldspar, and a poorly crystalline phase. Palygorskite fibers and fiber bundles were developed authigenically on euhedral or subhedral calcite crystals of the caliche units and at the edges of smectite flakes in the caliche host-rocks or sediments. Intense, continuous evaporation of subsurface soil-water resulted in an increase in pH and the dissolution of detrital smectite within the red mudstones and alluvial red soils that enclose the isolated caliche forms, and caused an increase in the Al+Fe and Mg/Ca ratio, favoring the formation of palygorskite under alkaline conditions. The calcium required for caliche formation may have originated from eolian dust, detrital carbonate minerals, and/or other caliche materials, which are dissolved by carbonic acid.

The uptake of Sr and Cs by 2 types of aluminum pillared layered clays (Al-PILC), a reference sample (AZA) and a specially tailored sample (FRAZA), were investigated. The AZA sample was prepared from air-dried precursors and the FRAZA sample from freeze-dried precursors. X-ray diffraction (XRD), pore and grain size measurements revealed that freeze-drying leads to a very fine-grained material with substantial mesoporosity. In contrast, air-drying results in coarse grains and an essentially microporous material. Four different methods were tested for restoring the cation exchange capacity (CEC) of the prepared PILCs. The most effective method proved to be exposing the material to ammonia fumes, then soaking it in a NaCl solution at pH =10. Strontium and Cs kinetic experiments were carried out with PILCs after restoring their CEC by this method. The results revealed 1 fast uptake component in both materials but with different relaxation times for each PILC.

Natural soils change by long-term pedogenetic mechanisms, but tillage effects can also strongly affect the evolution of soils, mainly their physicochemical properties. The present paper describes the impact of fertilizers and amendments on soil mineralogy in experimental plots, without plant interaction.

The soils of the 42 plots experiment at the INRA experimental station in Versailles (France) have been managed with fertilizers without plant growth since 1929. Strong changes in pH were observed and cation exchange capacities doubled between low and high pH (from 3.6 to 8.2). Strong acidification caused more evolution in the clay particle distribution without selective action on the clay composition.

While the clay content varied only slightly, the organic matter content changed considerably, decreasing with non-organic treatment and increasing in the plot with manure treatment. The major clay minerals in the experimental plots are two disordered illite-smectite mixed-layer minerals, with minor amounts of illite/mica and kaolinite. Most treatments effected only minor changes in clay mineralogy. However the illite (non-expandable mineral) content increased in plots with K addition either as KCl treatment or in manure amendments by increasing the illite content and the illite (non-expandable layer) content of the I-S minerals. Manure changed the I-S mineral to a greater extent.

The dehydration temperature of K-montmorillonite, obtained by ion exchange of a Na-mont-morillonite, was determined at pressures to 2 kbar, using high-pressure differential thermal analysis. Dehydration reactions were found at about 50° and 100°C above the liquid-vapor curve of water. At pressures above the critical point of water the dehydration temperatures increased only slightly. The temperature of the first dehydration reaction is 10°C higher than for Na-montmorillonite, indicating a slightly greater stability of the hydration shell around the potassium interlayer cation. The second dehydration reaction occurs at a slightly lower temperature. The data were used to determine the enthalpy of the dehydration ΔH(dh) and the bonding enthalpy of the interlayer water ΔH(iw) at 1 atm. The first dehydration reaction of the K-exchanged montmorillonite has a ΔH(dh) = 46.16 ± 0.06 kJ/mole and a ΔH(iw) = 7.8 ± 0.5 kJ/mole, whereas for the second reaction, ΔH(dh) = 56.7 ± 2 kJ/mole and ΔH(iw) = 19.8 ± 2 kJ/mole. These values compare with a ΔH(dh) = 46.8 ± 0.3 kJ/mole and a ΔH(iw) = 7.8 ± 0.5 kJ/mole for the first dehydration reaction of the Na-montmorillonite and a ΔH(dh) = 62.9 ± 2 kJ/mole and ΔH(iw) = 27.1 ± 2 kJ/mole for the second dehydration.

An experimentally determined Ca-Mg exchange isotherm of montmorillonite is reported. The selectivity coefficient of this exchange over a wide range of Mg saturation was calculated and found constant.

Standard free energies of exchange, thermodynamic equilibrium constants and activity coefficients of the exchangeable Ca and Mg ions in vermiculite and montmorillonite, were predicted from knowledge of the microstructure of these two clays, assuming that coulombic forces are the main ones playing a role in the interaction between the counterions and the charged clay surface. The standard free energies of exchange (ΔGCa°Mg = 238 cal/mole) predicted a preference for Ca in montmorillonite and a preference for Mg in vermiculite (ΔGCa°Mg = - 1665 cal/mole). The predicted thermodynamic equilibrium constants were compatible with the experimentally determined selectivity coefficients KsCaMg = 0·67 as compared with KsCaMg = 0·68 in montmorillonite, which remains constant over all the range of Mg saturation, and KCaMg = 16·7 as compared with KsCaMg = 13·9 in vermiculite at 95% Mg saturation. The activity coefficients of Ca and Mg counterions in montmorillonite were found to be and , respectively, and to remain constant. The activity coefficients of exchangeable Ca and Mg in vermiculite were found to be and , respectively, at an equivalent fraction of unity. The activity coefficient of exchangeable Mg increased as the saturation with Mg decreased, and was found to be 1·7 × 10-3 in the range of the low Mg saturation.

The microstructure, the isomorphic substitution and the surface charge density provided an understanding of the changes taking place in the activity coefficients of the counterions.

Electron spin resonance (ESR) analysis of Cu2+-hectorite suspensions provides evidence for the surface-induced hydrolysis of Cu(H2O)62+ at low pH and surface-inhibited hydrolysis (or precipitation) at high pH. Dehydration of the hectorite by heating to 110°C appears to promote hydrolysis in high pH clays further. Heating to even higher temperatures removes ligand water from Cu2+, allowing the metal ion to coordinate with silicate oxygen atoms. The planar Cu(H2O)42+ ion predominates in the interlamellar regions of hectorite that has been air dried or heated to temperatures of 110°C or lower, but more extreme thermal treatment changes the apparent orientation of the Cu2+-ligand axes as some or all of the four water ligands are removed, A loss in ESR signal intensity upon heating Cu2+-hectorite above 110°C is evidence for lowered symmetry of the dehydrated, surface-coordinated Cu2+ ion.

Lode, a dioctahedral illite-rich clay from Latvia belonging to the mica group of clay minerals, undergoes thermal transformation via a series of structurally disordered intermediate phases. Despite containing high levels of paramagnetic Fe substituted into the octahedral sites, 29Si and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectra of sufficient quality are obtained to resolve different structural units, showing clearly defined structural changes which occur in the sample during calcination to 1200 °C. However, Fe plays a significant role in broadening the Al signal, with integrated peak intensities decreasing as temperature increases. Significant differences are revealed in the thermal decomposition process by NMR spectra between pyrophyllite, Ca-montmorillonite and illite clays, possibly due to the different cations present in the interlayer. It has also been shown for illite that no structural differences at the atomic level occur when the dwell time at a particular temperature is varied and no difference is observed between samples that have different thermal histories; however, a minor effect of particle size and surface area is visible in the NMR data.